Depends on wether it is a Poltergeist or a standard haunting. Poltergesits usually are as the previous post stated attracted to the strong energies of powerful people or children. They will usually go away on there own after a short time. Hauntings on the other hand are a little bit more fixed based. A place can be the home of spirits for years or more. The best bet with a haunting is to have an exercism done on the place. Anyone who knows what they are doing can do one for you.
I don't know, I have had one around me for the last fifty years or so, it likes to hide things from me.
Example, working on a car or something and drop a tool/wrench. Look under the car and not there. Go to the tool box to get another wrench and the one that fell is there in the box. That has happened hundreds of times.
I have not honestly tried any way to get rid of it, so don't know how to get rid of one, but one of the banishing spells might work,or simply telling it to go away might do the trick.